Preheat oven to 350º F. Place two racks in the oven; the top for the cheesecake and the bottom for a water bath (2 inches of warm water in a roasting pan).
To prepare the crust:
Combine crumbs, nuts and lemon peel. Stir in butter until thoroughly blended. Press mixture firmly against bottom of 9″ springform pan or a 10” round cake pan lined with parchment paper.
To prepare the filling:
In a medium bowl, whip egg whites until stiff peaks form. In a large bowl, beat cream cheese until creamy. Gradually add agave syrup; blend. Add vanilla, cornstarch and lemon peel. Blend well. Add egg yolks, one at a time, scraping the bowl after each addition. Beat at medium speed for 5 minutes, until nice and smooth. Fold in the sour cream. Fold in egg whites. Pour all into the springform pan.
Bake 45-50 minutes until cheesecake is lightly browned on the edges. Turn off the oven and leave cheesecake in the oven for 1 hour with door closed. After 1 hour, open door slightly and leave in oven for a further 10 minutes more. Remove cheesecake and allow to cool in pan for an additional hour.
Place in the refrigerator, uncovered, for at least 3 hours. Remove from springform pan before serving.